Tuesday, November 2, 2010

April 16th, 2009

Klagenfurt, Austria. Most Self-Erecting tower cranes have a derricking crane off the mast that allows for counter weight removal. In most cases it's slow and clumsy and requires that the weights be double handled. So in every case but one, (we were 19 stories up on a building) we have always used an assist crane or fork lift to add or remove weights. In this case, they were using a articulating crane with a fixed hook to remove the weights. During the operation the weights were caused to topple injuring one worker and destroying the cab of the crane. 

The crane appears to be a Potain HDT 80 (U.S. Designation). Each of the weights weighs 6300 lbs or roughly 2860 kg and there are 13 of them. On the side they have ladder rungs that form a ladder that becomes quite tall and those rungs lead to the top where you'll find two picking eyes. The picking eyes are embedded into the concrete on top of a raised section that mates to a recessed area on the bottom of the next weight. This eliminates the needs for tie downs and aligns the weights automatically. 

The difficulty in removing these weights is that when you use a fixed hook on the end of a boom, you must be cognizant of the boom angle and keeping the picking eyes from binding on the recessed area. The higher up the weights, the steeper the boom angle is. So as you boom up to lift the weights, you decrease the radius quicker than you gain clearance. The solution is to extend the boom in order to gain clearance. The same is true with Tele-Handler Forklifts. In this case it would seem that someone wasn't paying enough attention to the boom angle on the load an pulled the remainder of the load on to the truck crane itself. The concept is basic, but if it's your first time, it's better to ask questions, give up a modicum of appearance of expertise, and have everyone go home healthy and alive. Link to story.

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